From ce23ecbd28487824bbae5ae3d9f20b7781e6cd32 Mon Sep 17 00:00:00 2001
From: Aaron LI <aaronly.me@outlook.com>
Date: Sun, 8 Jan 2017 13:41:05 +0800
Subject: halo.py: Force a minimal value on acceleration coefficient

To avoid the too small (or zero) values for the diffusion coefficient of
the Fokker-Planck equation.

Also change config "extragalactic/halo/pmax" from 1e4 to 1e5
---
 fg21sim/extragalactic/clusters/halo.py   | 26 +++++++++++++++++++++++++-
 fg21sim/extragalactic/clusters/solver.py |  2 +-
 2 files changed, 26 insertions(+), 2 deletions(-)

(limited to 'fg21sim/extragalactic/clusters')

diff --git a/fg21sim/extragalactic/clusters/halo.py b/fg21sim/extragalactic/clusters/halo.py
index 072cdff..6adfba5 100644
--- a/fg21sim/extragalactic/clusters/halo.py
+++ b/fg21sim/extragalactic/clusters/halo.py
@@ -447,6 +447,27 @@ class HaloSingle:
         Calculate the electron-acceleration coefficient at arbitrary
         redshift, by interpolating the coefficients calculated at every
         merger redshifts.
+
+        Parameters
+        ----------
+        z : float
+            Redshift where to calculate the acceleration coefficient.
+
+        Returns
+        -------
+        chi : float
+            The calculated electron-acceleration coefficient.
+            (unit: Gyr^-1)
+
+        XXX/NOTE
+        --------
+        This coefficient may be very small and even zero, then the
+        diffusion coefficient of the Fokker-Planck equation is  thus
+        very small and even zero, which cause problems for calculating
+        some quantities (e.g., w(x), C(x)) and wrong/invalid results.
+        To avoid these problems, force the minimal value of this
+        coefficient to be 1/(10*t0), which t0 is the present-day age
+        of the universe.
         """
         if not hasattr(self, "_coef_acceleration_interp"):
             # Order the merger events by decreasing redshifts
@@ -454,9 +475,12 @@ class HaloSingle:
             redshifts = np.array([ev["z"] for ev in mevents])
             chis = np.array([self._chi_at_zidx(zidx, mevents)
                              for zidx in range(len(redshifts))])
+            # XXX: force a minimal value instead of zero or too small
+            chi_min = 1.0 / (10 * self.cosmo.age0)
+            chis[chis < chi_min] = chi_min
             self._coef_acceleration_interp = scipy.interpolate.interp1d(
                     redshifts, chis, kind="linear",
-                    bounds_error=False, fill_value=0.0)
+                    bounds_error=False, fill_value=chi_min)
             logger.info("Interpolated acceleration coefficients w.r.t. z")
         return self._coef_acceleration_interp(z)
 
diff --git a/fg21sim/extragalactic/clusters/solver.py b/fg21sim/extragalactic/clusters/solver.py
index c1f01d1..9d4a781 100644
--- a/fg21sim/extragalactic/clusters/solver.py
+++ b/fg21sim/extragalactic/clusters/solver.py
@@ -58,7 +58,7 @@ class FokkerPlanckSolver:
 
     u(x,t) : distribution/spectrum w.r.t. x at different times
     B(x,t) : advection coefficient
-    C(x,t) : diffusion coefficient (>=0)
+    C(x,t) : diffusion coefficient (>0)
     Q(x,t) : injection coefficient (>=0)
 
     References
-- 
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